The invention is based on a process for the production of fiber-reinforced components or semifinished products, where fibers are saturated with monomer.
Fiber-reinforced composite materials are usually produced by inserting the fibers into a suitable mold and then casting the molten polymer around said fibers. Alternatively it is also possible to cast, around the fibers, a monomer solution, polymerization of which is completed in the mold. A disadvantage here, however, in particular in the case of dense fiber packing, is that the high viscosity of the polymer melts prevents complete wetting of the fibers, with resultant weakness in the material. The monomer-casting process usually relates to thermoset polymers, but with the attendant disadvantage that continuous processing is not possible because the components produced from the fiber-reinforced composite material always have to harden in the mold. Once the casting process and hardening process have taken place, shaping has already occurred. This method cannot easily be used to produce semifinished products that are amenable to further processing. Prepregs based on partially hardened epoxy resins are known, but these have to be stored at low temperature in order to avoid undesired hardening during storage. The hardening process in the mold moreover limits the possible throughput, and this is a disadvantage in particular when mass production of components is required.
The wetting of fibers with a monomer for a fiber-reinforced thermoplastic polymer is disclosed in DE-A 196 02 638. Here, a reinforcement-fiber structure, for example a woven fabric or individual layers of continuous-filament fibers, is saturated with a melt made of lactam comprising activator, catalyst, and optionally other additives. Saturation with the lactam melt is followed by heating to reaction temperature, and the lactam polymerizes to give the corresponding polyamide. In order to avoid dripping of molten lactam from the reinforcement-fiber structure, the polymerization step has to be carried out immediately after the saturation process. This has the disadvantage that the polymerization step limits the speed of processing. If relatively large numbers of parts are to be produced it is always necessary to provide systems in which the reinforcement-fiber structures are first saturated with the lactam melt and then are molded to give the molding. DE-A 196 02 638 moreover discloses production of moldings made of flat, fiber-reinforced elements by first using saturation of textile structures with lactam, and full polymerization to produce the flat, fiber-reinforced elements, and then subjecting the resultant fiber-reinforced elements to a forming process in a heated mold to give the molding.
WO-A 2012/116947 discloses that the limitation of speed of processing caused by the polymerization step can be minimized by first saturating the fiber structure with a monomer and then cooling, thus solidifying the monomer without full polymerization. The cooled structures are cut to size to give a flat semifinished product which can then be further processed.
The cutting-to-size and the further processing produce offcut as waste. Waste is also produced in the production of components via injection-molding processes, an example being the polymer hardened in the runners. The offcut produced during the cutting-to-size of semifinished products that have not fully polymerized comprises monomer that has not fully polymerized, whereas the monomer in the offcut produced during the production of finished parts or in the offcut produced during the injection-molding process is fully polymerized monomer.
Because of the different degree of polymerization, and because of the fibers comprised, the offcut can at present be used only with restrictions, and in particular only for the production of low-quality components. Although the offcut comprises valuable raw materials, its composition usually determines that it is sent for disposal.